OK before I try unsticking, here's the followup to strace with the longer lines:
PID 6500:
read(0</tmp/run/cake-autorate/primary/log_fifo>, "9", 1) = 1
read(0</tmp/run/cake-autorate/primary/log_fifo>, "0", 1) = 1
read(0</tmp/run/cake-autorate/primary/log_fifo>, "5", 1) = 1
read(0</tmp/run/cake-autorate/primary/log_fifo>, "4", 1) = 1
read(0</tmp/run/cake-autorate/primary/log_fifo>, ";", 1) = 1
read(0</tmp/run/cake-autorate/primary/log_fifo>, " ", 1) = 1
read(0</tmp/run/cake-autorate/primary/log_fifo>, "1", 1) = 1
read(0</tmp/run/cake-autorate/primary/log_fifo>, "0", 1) = 1
read(0</tmp/run/cake-autorate/primary/log_fifo>, "0", 1) = 1
read(0</tmp/run/cake-autorate/primary/log_fifo>, "0", 1) = 1
read(0</tmp/run/cake-autorate/primary/log_fifo>, "0", 1) = 1
read(0</tmp/run/cake-autorate/primary/log_fifo>, "\n", 1) = 1
rt_sigprocmask(SIG_BLOCK, [CHLD], [], 16) = 0
rt_sigprocmask(SIG_SETMASK, [], NULL, 16) = 0
open("/var/log/cake-autorate.primary.log", O_WRONLY|O_CREAT|O_APPEND|O_LARGEFILE, 0666) = 3</tmp/log/cake-autorate.primary.log>
fcntl64(1</dev/null>, F_GETFD) = 0
fcntl64(1</dev/null>, F_DUPFD, 10) = 13</dev/null>
fcntl64(1</dev/null>, F_GETFD) = 0
fcntl64(13</dev/null>, F_SETFD, FD_CLOEXEC) = 0
dup2(3</tmp/log/cake-autorate.primary.log>, 1</dev/null>) = 1</tmp/log/cake-autorate.primary.log>
close(3</tmp/log/cake-autorate.primary.log>) = 0
writev(1</tmp/log/cake-autorate.primary.log>, [{iov_base="LOAD; 2023-01-26-12:41:06; 1674758466.597987; 1674758466.597209; 57; 106; 89054; 10000", iov_len=86}, {iov_base="\n", iov_len=1}], 2) = 87
dup2(13</dev/null>, 1</tmp/log/cake-autorate.primary.log>) = 1</dev/null>
fcntl64(13</dev/null>, F_GETFD) = 0x1 (flags FD_CLOEXEC)
close(13</dev/null>) = 0
rt_sigprocmask(SIG_BLOCK, NULL, [], 16) = 0
ioctl(0</tmp/run/cake-autorate/primary/log_fifo>, TIOCGWINSZ, 0x7fac2330) = -1 ENOTTY (Not a tty)
_llseek(0</tmp/run/cake-autorate/primary/log_fifo>, 0, 0x7fac2330, SEEK_CUR) = -1 ESPIPE (Invalid seek)
read(0</tmp/run/cake-autorate/primary/log_fifo>, ^Cstrace: Process 6500 detached
<detached ...>
PID 6523:
rt_sigprocmask(SIG_BLOCK, NULL, [], 16) = 0
ioctl(0</tmp/run/cake-autorate/primary/dl_shaper_rate_kbps>, TIOCGWINSZ, 0x7fac19f8) = -1 ENOTTY (Not a tty)
_llseek(0</tmp/run/cake-autorate/primary/dl_shaper_rate_kbps>, 0, [0], SEEK_CUR) = 0
read(0</tmp/run/cake-autorate/primary/dl_shaper_rate_kbps>, "89054", 4096) = 5
read(0</tmp/run/cake-autorate/primary/dl_shaper_rate_kbps>, "", 4096) = 0
dup2(12</dev/null>, 0</tmp/run/cake-autorate/primary/dl_shaper_rate_kbps>) = 0</dev/null>
fcntl64(12</dev/null>, F_GETFD) = 0x1 (flags FD_CLOEXEC)
close(12</dev/null>) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x77e14000
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x77e12000
munmap(0x77e14000, 4096) = 0
munmap(0x77e12000, 4096) = 0
rt_sigprocmask(SIG_BLOCK, [CHLD], [], 16) = 0
rt_sigprocmask(SIG_SETMASK, [], NULL, 16) = 0
open("/var/run/cake-autorate/primary/ul_shaper_rate_kbps", O_RDONLY|O_LARGEFILE) = 3</tmp/run/cake-autorate/primary/ul_shaper_rate_kbps>
fcntl64(0</dev/null>, F_GETFD) = 0
fcntl64(0</dev/null>, F_DUPFD, 10) = 12</dev/null>
fcntl64(0</dev/null>, F_GETFD) = 0
fcntl64(12</dev/null>, F_SETFD, FD_CLOEXEC) = 0
dup2(3</tmp/run/cake-autorate/primary/ul_shaper_rate_kbps>, 0</dev/null>) = 0</tmp/run/cake-autorate/primary/ul_shaper_rate_kbps>
close(3</tmp/run/cake-autorate/primary/ul_shaper_rate_kbps>) = 0
rt_sigprocmask(SIG_BLOCK, NULL, [], 16) = 0
ioctl(0</tmp/run/cake-autorate/primary/ul_shaper_rate_kbps>, TIOCGWINSZ, 0x7fac1a28) = -1 ENOTTY (Not a tty)
_llseek(0</tmp/run/cake-autorate/primary/ul_shaper_rate_kbps>, 0, [0], SEEK_CUR) = 0
read(0</tmp/run/cake-autorate/primary/ul_shaper_rate_kbps>, "10000", 4096) = 5
read(0</tmp/run/cake-autorate/primary/ul_shaper_rate_kbps>, "", 4096) = 0
dup2(12</dev/null>, 0</tmp/run/cake-autorate/primary/ul_shaper_rate_kbps>) = 0</dev/null>
fcntl64(12</dev/null>, F_GETFD) = 0x1 (flags FD_CLOEXEC)
close(12</dev/null>) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x77e14000
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x77e12000
munmap(0x77e14000, 4096) = 0
munmap(0x77e12000, 4096) = 0
statx(AT_FDCWD</>, "/var/run/cake-autorate/primary/log_fifo", AT_STATX_SYNC_AS_STAT, STATX_BASIC_STATS, {stx_mask=STATX_BASIC_STATS|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFIFO|0644, stx_size=0, ...}) = 0
open("/var/run/cake-autorate/primary/log_fifo", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE, 0666) = 3</tmp/run/cake-autorate/primary/log_fifo>
fcntl64(1</tmp/run/cake-autorate/primary/log_fifo>, F_GETFD) = 0
fcntl64(1</tmp/run/cake-autorate/primary/log_fifo>, F_DUPFD, 10) = 12</tmp/run/cake-autorate/primary/log_fifo>
fcntl64(1</tmp/run/cake-autorate/primary/log_fifo>, F_GETFD) = 0
fcntl64(12</tmp/run/cake-autorate/primary/log_fifo>, F_SETFD, FD_CLOEXEC) = 0
dup2(3</tmp/run/cake-autorate/primary/log_fifo>, 1</tmp/run/cake-autorate/primary/log_fifo>) = 1</tmp/run/cake-autorate/primary/log_fifo>
close(3</tmp/run/cake-autorate/primary/log_fifo>) = 0
munmap(0x77e15000, 23) = 0
open("/etc/TZ", O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_CLOEXEC) = 3</tmp/TZ>
fstat64(3</tmp/TZ>, {st_mode=S_IFREG|0644, st_size=23, ...}) = 0
mmap2(NULL, 23, PROT_READ, MAP_SHARED, 3</tmp/TZ>, 0) = 0x77e15000
close(3</tmp/TZ>) = 0
munmap(0x77e15000, 23) = 0
open("/etc/TZ", O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_CLOEXEC) = 3</tmp/TZ>
fstat64(3</tmp/TZ>, {st_mode=S_IFREG|0644, st_size=23, ...}) = 0
mmap2(NULL, 23, PROT_READ, MAP_SHARED, 3</tmp/TZ>, 0) = 0x77e15000
close(3</tmp/TZ>) = 0
writev(1</tmp/run/cake-autorate/primary/log_fifo>, [{iov_base="LOAD; 2023-01-26-12:41:39; 1674758499.964866; 1674758499.964051; 26; 10; 89054; 10000", iov_len=85}, {iov_base="\n", iov_len=1}], 2) = 86
dup2(12</tmp/run/cake-autorate/primary/log_fifo>, 1</tmp/run/cake-autorate/primary/log_fifo>) = 1</tmp/run/cake-autorate/primary/log_fifo>
fcntl64(12</tmp/run/cake-autorate/primary/log_fifo>, F_GETFD) = 0x1 (flags FD_CLOEXEC)
close(12</tmp/run/cake-autorate/primary/log_fifo>) = 0
rt_sigprocmask(SIG_BLOCK, [CHLD], [], 16) = 0
rt_sigprocmask(SIG_SETMASK, [], NULL, 16) = 0
open("/var/run/cake-autorate/primary/max_wire_packet_rtt_us", O_RDONLY|O_LARGEFILE) = 3</tmp/run/cake-autorate/primary/max_wire_packet_rtt_us>
fcntl64(0</dev/null>, F_GETFD) = 0
fcntl64(0</dev/null>, F_DUPFD, 10) = 12</dev/null>
fcntl64(0</dev/null>, F_GETFD) = 0
fcntl64(12</dev/null>, F_SETFD, FD_CLOEXEC) = 0
dup2(3</tmp/run/cake-autorate/primary/max_wire_packet_rtt_us>, 0</dev/null>) = 0</tmp/run/cake-autorate/primary/max_wire_packet_rtt_us>
close(3</tmp/run/cake-autorate/primary/max_wire_packet_rtt_us>) = 0
rt_sigprocmask(SIG_BLOCK, NULL, [], 16) = 0
ioctl(0</tmp/run/cake-autorate/primary/max_wire_packet_rtt_us>, TIOCGWINSZ, 0x7fac2160) = -1 ENOTTY (Not a tty)
_llseek(0</tmp/run/cake-autorate/primary/max_wire_packet_rtt_us>, 0, [0], SEEK_CUR) = 0
read(0</tmp/run/cake-autorate/primary/max_wire_packet_rtt_us>, "1334", 4096) = 4
read(0</tmp/run/cake-autorate/primary/max_wire_packet_rtt_us>, "", 4096) = 0
dup2(12</dev/null>, 0</tmp/run/cake-autorate/primary/max_wire_packet_rtt_us>) = 0</dev/null>
fcntl64(12</dev/null>, F_GETFD) = 0x1 (flags FD_CLOEXEC)
close(12</dev/null>) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x77e14000
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x77e12000
munmap(0x77e14000, 4096) = 0
munmap(0x77e12000, 4096) = 0
rt_sigprocmask(SIG_BLOCK, [CHLD], [], 16) = 0
rt_sigprocmask(SIG_SETMASK, [], NULL, 16) = 0
statx(AT_FDCWD</>, "/sys/class/net/ifb4eth0/statistics/tx_bytes", AT_STATX_SYNC_AS_STAT, STATX_BASIC_STATS, {stx_mask=STATX_BASIC_STATS|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0444, stx_size=4096, ...}) = 0
open("/dev/null", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE, 0666) = 3</dev/null>
fcntl64(2<pipe:[6055]>, F_GETFD) = 0
fcntl64(2<pipe:[6055]>, F_DUPFD, 10) = 12<pipe:[6055]>
fcntl64(2<pipe:[6055]>, F_GETFD) = 0
fcntl64(12<pipe:[6055]>, F_SETFD, FD_CLOEXEC) = 0
dup2(3</dev/null>, 2<pipe:[6055]>) = 2</dev/null>
close(3</dev/null>) = 0
open("/sys/class/net/ifb4eth0/statistics/tx_bytes", O_RDONLY|O_LARGEFILE) = 3</sys/devices/virtual/net/ifb4eth0/statistics/tx_bytes>
fcntl64(0</dev/null>, F_GETFD) = 0
fcntl64(0</dev/null>, F_DUPFD, 10) = 13</dev/null>
fcntl64(0</dev/null>, F_GETFD) = 0^Cstrace: Process 6523 detached